The present invention relates to a cutting tool having a throw-away tip and, more particularly, to a resource-saving type cutting tool.
A throw-away tip to function as a cutting edge of a bit tool generally has a variety of merits, e.g., a lower cost per a cutting edge than a resharpening type brazed tip, less handling time for replacing a worn tip with a new tip, reproducibility in the positional relationship between a bit-holder after replacement and a new tip to be similarly retained to the state before the replacement, and has hence a wide application in an industrial field. Since the throw-away tip is, however, formed of expensive materials such as, tungsten, cobalt, etc., it has a disadvantage of expensive cost.
FIG. 1A is a perspective view showing a conventional throw-away tip integral with a bit-holder. As shown in FIG. 1A, a throw-away tip 1 has a through hole 5 to be engaged with a tip locking pin 4 tiltably mounted with a shim 3 of a bit-holder 2. This pin 4 is, as shown in FIG. 2, inclined toward the wall surface 7 at the tip seat side of the bit-holder 2 by rotating and implanting a clamping screw 6. When this tip 1 is attached to the bit-holder 2, the tip locking pin 4 is inserted into the mounting hole 5 to arrange the tip 1 on the shim 3, and the clamping screw 6 is turned and implanted. The locking pin 4 is inclined by this turning toward the wall surface 7, the tip 1 is urged onto the wall surface 7, and is locked onto the bit-holder 2. The throw-away tip 1 thus mounted at the bit-holder 2 is contacted with a workpiece to cut the same. In ordinary cutting work, a relief face wear 8a and a rake face wear 8b will respectively occur on a relief face 1a and a rake face 1b both forming a cutting edge of the tip 1, as shown in FIGS. 1A and 1B. The width V.sub.B of the relief face wear 8a which relates directly to the dimensional accuracy of the workpiece and the roughness of the finished surface of the workpiece is normally less than 0.5 mm, and a relatively small amount of wear of the cutting edge takes place at the extremely restricted parts.
In cutting theory, in case, for example, of an ordinary three-dimensional cutting, as shown in FIG. 3, of a cylindrical workpiece 9, a cutting resistance force P0 can be divided into a main component P1 of force, a feeding component P2 of force and a back component P3 of force. The magnitudes of the respective components of force normally depend on the material of the workpiece 9, the shapes of the tip 1 and the bit-holder 2, the cutting conditions, etc. and the main component P1 of force is commonly prominent. It is appreciated from this that the size and hence the width of the tip 1 along a direction of the feeding component P2 of force is not so necessarily required as the size and hence the thickness of the tip 1 along a direction of the main component P1. However, in the conventional tip 1, the width of the tip 1 is normally larger than the thickness of the tip due to the feasibility of locking to the bit-holder 2 and to the interchangeability of the tip. As described above, an effort to positively reduce the capacity of the tip rationally as much as possible to save resources is not carried out in the conventional throw-away tip by considering the wearing state and the cutting resistance.